Numerics of the Elements. 549 



quality. But a new source of oxygen, in a substance capable 

 of progressive decomposition, is still to be desired. 



It would appear to be in all cases essential to determine 

 the effect of light. 



The numeric of oxygen has been at various times taken as 

 100, 1, 15*96, 15*88, and 16. At present there are two 

 scales in use, viz. = 16, H = 1-008; and = 15'88, H=l. 

 When the composition of water is ultimately decided, these 

 ratios may undergo some change. But none of the values 

 proposed has any special physical meaning as a ground for 

 preference in practical use. 



The value = 15*94, adopted in this memoir, has the 

 advantage of lying exactly midway between — and so, perhaps, 

 conciliating — the modern hydrogen and oxygen scales. It 

 is calculated from rigorous mathematical conditions, and 

 includes all known elements, excepting hydrogen ; it is, con- 

 sequently, inter dependently related to all the elements. 

 There is a reason, therefore, for preferring this value ; or, 

 at any rate, some value similarly calculated. It may, indeed, 

 be said that, within the limits of experimental error, the 

 practical value is in fact = 15*94. 



Linear periodicity is no longer admissible. 



Clarke comments on his own table of numerics (1897) in 

 these terms : — " In most cases even the first decimal is 

 uncertain ; and in some instances whole units may be in 

 doubt." The determinations are, in fact, so much affected 

 by constant error, that their probable error is seldom worth 

 calculating. Of all constant errors, the most important 

 would seem due to the fact, now in course of general accept- 

 ance, that pure chemical substances do not interact with 

 each other *. 



* Amongst common metals, the numeric of zinc is still much too un- 

 certain. For samarium I have taken Bettendorff's value ; for zirconium, 

 Bailey's. The mean of Hardin's, Keiser's, and Joly & Leidie"s not too 

 concordant results has been accepted for palladium. Other authorities 

 are Meyer and Lenker, selenium (mean) ; Seubert & Kobbe, rhodium ; 

 Morse & Jones, cadmium • Kothner and Pellini, tellurium (mean) ; Jones 

 & Brauner and Pavlicek, lanthanum (mean); Jones and Van Scheie, 

 praseodidymium (mean) ; Jones, neodidymium ; Cleve, ytterbium ; Seubert, 

 osmium and rhodium ; Classen, bismuth ; Mallet, gold. Erbia and terbia 

 remain in considerable doubt. In some cases of modern recalculation 

 confusion has arisen from taking' former numbers — at one time announced 

 as " on the hydrogen scale (1*00)," — as being on the present hydrogen 

 scale (1-008). 



